This is the 93rd most frequent Polish word.
siebie
"Oneself" or "yourself" (reflexive pronoun).
Reflexive usage, indicating something internal about the subject.
Znalazłem w sobie nowe hobby.
I found a new hobby within myself.
Reflexive imperative, directing the action towards the person being addressed.
Pamiętaj, żeby dbać o siebie.
Remember to take care of yourself.
Reflexive usage, referring to the person who is the subject of the sentence.